I did data recovery and data archiving a bit in the past, here are some things to be aware of:
1. Optical discs will go bad over time, either the plastic will become opaque or they will oxidize between the layers, you can look up "bit rot" for more information but be warned that term has been abused a bit and applied to other things.
2. If you really want to use optical discs be aware that there is a huge difference in quality between different manufacturers. Also many name brands will use discs from different manufacturers so if you walk into an office supply store and buy the store brand discs they may have been manufactured in a different part of the world by a different company than the ones you got in the same store a week earlier. Some websites such as videohelp.com have done reviews of burned disc readability after time has passed, the short answer is for single layer dvdr discs use dvd+r discs made by Taiyo Yuden (now often sold under the JVC name). For dual-layer discs it's a little more muddied but Verbatim is usually a safe choice.
3. Data stored on flash memory (ssd or usb flash drives) will degrade over time, this is because the data is stored in cells that are either charged or discharged to represent a 1 or 0 (charged is zero for whatever reason). Over time electrons will escape these cells making it harder to distinguish between a one or zero, providing power to the drive will not recharge these cells, you have to actually re-write the data. It is not clear how much of an issue this is because the drives have not been around long enough, the estimates are anywhere from a couple years to a decade. I suspect there is wide variation between different qualities of flash memory since this is true of other reliability metrics. This isn't a huge deal for most people but I would say don't put the only copy of your documents on a usb flash drive, throw it in a drawer, and count on being able to read it perfectly in 20 years.
4. Fire safes are generally designed to protect against paper inside the safe igniting, optical discs and other forms of digital storage may be destroyed at far lower temperatures. I prefer safe deposit boxes at a bank. Obviously this is less convenient than being in your place of residence but they have the advantage of being more physically secure, climate controlled, and off-site. Prices and sizes available vary widely at different banks so call a couple in your area. I have seen as low as $20/year for a 3"x5"x36" in my area.
If it's a small amount of personal data (tax documents, personal projects, emails) stick it in an encrypted archive if you care about it being encrypted (7zip is an easy to use, cross-platform, open source, well vetted option). Then put it on a couple different forms of media, such as a spinning magnetic drive in an anti-static bag, and an optical disc. Then store these off site somewhere such as at a friend or relative's house, or in a bank safe deposit box. And also stick a copy online somewhere such as on your google documents account or a dropbox account, this is an especially good option if you have encrypted it first.
If it's a large amount of data like full disk backups or a huge photo archive that are very important to you or your business stick it on a spinning magnetic hard drive, put it in an anti-static bag, and put it in a bank safe deposit box. Spinning magnetic drives are very stable if stored in a temperature/humidity controlled environment, more so than optical or flash memory. They are also still the king when it comes to dollar per megabyte (a good quality 2TB sata drive can be had for $80-$100 right now) and sata ports are likely to be common on all motherboards for at least another decade.
One last thing which will seem obvious, label every backup drive/disc/whatever, even if it's just a post-it note. You will not remember exactly what it is 5 years down the road.
happy archiving :)